A typical alternating-current surface discharge type panel used as a plasma display panel (hereinafter referred to as “panel”) has many discharge cells between a front plate and a back plate that are faced to each other. The front plate has the following elements:                a plurality of display electrode pairs disposed in parallel on a front glass substrate; and        a dielectric layer and a protective layer for covering the display electrode pairs.        
Here, each display electrode pair is formed of a pair of scan electrode and sustain electrode. The back plate has the following elements:                a plurality of data electrodes disposed in parallel on a back glass substrate;        a dielectric layer for covering the data electrodes;        a plurality of barrier ribs disposed on the dielectric layer in parallel with the data electrodes; and        phosphor layers disposed on the surface of the dielectric layer and on side surfaces of the barrier ribs.The front plate and back plate are faced to each other so that the display electrode pairs and the data electrodes three-dimensionally intersect, and are sealed. Discharge gas containing xenon at a partial pressure of 5%, for example, is filled into a discharge space in the sealed product. Discharge cells are disposed in intersecting parts of the display electrode pairs and the data electrodes. In the panel having this structure, ultraviolet rays are emitted by gas discharge in each discharge cell. The ultraviolet rays excite respective phosphors of red (R), green (G), and blue (B) to emit light, and thus provide color display.        
A subfield method is generally used as a method of driving the panel. In this method, one field period is divided into a plurality of subfields, and the subfields at which light is emitted are combined, thereby performing gradation display.
Each subfield has an initializing period, an address period, and a sustain period. In the initializing period, initializing discharge occurs, a wall charge required for a subsequent addressing operation is formed on each electrode, and a priming particle (excitation particle as a detonating agent for discharge) for stably causing address discharge is generated. In the address period, addressing pulse voltage is selectively applied to a discharge cell where display is to be performed to cause address discharge, thereby forming a wall charge (hereinafter, this operation is referred to as “addressing”). In the sustain period, sustain pulse voltage is alternately applied to the display electrode pairs formed of the scan electrodes and the sustain electrodes, sustain discharge is caused in the discharge cell having performed address discharge, and a phosphor layer of the corresponding discharge cell is light-emitted, thereby displaying an image.
Of the subfield method, a new driving method is disclosed where light emission that is not related to gradation display is minimized and the contrast ratio is improved. In this driving method, the initializing discharge is performed using a gradually varying voltage waveform, and the initializing discharge is selectively applied to the discharge cell having performed sustain discharge. Thus, light emission that is not related to the gradation display is minimized, and the contrast ratio is improved.
In this driving method, for example, in the initializing period of one of a plurality of subfields, an initializing operation (hereinafter referred to as “all-cell initializing operation”) of causing initializing discharge in all discharge cells is performed. In the initializing period of the other subfields, an initializing operation (hereinafter referred to as “selection initializing operation”) of causing initializing discharge in only a discharge cell having performed sustain discharge is performed. Thanks to this driving manner, the light emission that is not related to the image display is determined only by light emission following the discharge of the all-cell initializing operation. As a result, the luminance (hereinafter referred to as “black luminance”) in a black display region is provided only by feeble light emission by the all-cell initializing operation, and an image of high contrast can be displayed. This driving method is disclosed in patent document 1, for example.
The definition and screen size of the panel have been recently increased, and hence the quality of the display image has been required to be further improved in the plasma display device. However, the discharge characteristic of the panel varies (hereinafter referred to as “variation with time”) according to the accumulative time (hereinafter referred to as “current-flow accumulative time”) of time when current is applied to the panel. The progress rate of the variation with time of the discharge characteristic of the panel depends on the image displayed on the panel. Therefore, it is not easy to optimize the control of stably causing discharge regardless of the current-flow accumulative time and the image displayed on the panel.    [Patent document 1] Japanese Patent Unexamined Publication No. 2000-242224